A treatment for removal of foreign material from material such as powder, particles or liquid, filtration or dehydration has heretofore been made to use an oscillating motor and the like, by which the foreign material is removed in such a manner that the screen oscillates. In a case that the screen is broken during treatment of the material, an operator must stop the screening operation and replace the broken screening device into the new one to start the operation again. The broken screening device is prepared for the following operation by fixing a separate screen.
However, a plurality of screening devices are commonly used in a conventional way by an expert pertaining to the art of the screening. The operator must replace the broken screen into the new one and spend a plenty of time. It also requires a high degree of skill to attach the screen to the frame uniformly. Therefore, the research for the cause of breakage of the screen clarifies that it causes some constructional defects of the screening device rather than the scratch or wear by the material as having heretofore been known to the expert and the screen breaks mainly in the vicinity of the portion fastened by the bolts and the like.
Therefore, this applicant had filed an application concerning an invention entitled to "A screen frame" (Japanese Utility Model Application No. 36444 of 1985) as disclosed in FIG. 4, so as to eliminate the above-noted problem.
This type of the screening device has an excellent feature that the screen (a) can be uniformly attached to the frame (b) in an extremely short period and the screening device can be continuously operated over a long period, compared with a conventional one.
However, when the inflatable tube (c) is inflated by pressured gas, the tube (c) will press the screen (a) against the inner surface (d) of the holder member (e) as indicated by an alternate long and two dashes line in FIG. 4. As a result, it has become evident that the screen (a) has been broken by the wear at the portion touching the holder member (e).